1. Field of the Invention
The present invention relates to a process for determining the relative velocity in the radial direction between two moving objects, using linear frequency modulation with continuous frequency sweeps, a transmitted signal being multiplied by a received signal for the attainment of a resultant received signal, the phase change of which over a certain time is used to determine the relative velocity.
2. Description of Related Art
A problem in determining the velocity where linear frequency modulation is used is to be able clearly to determine the phase difference. The phase change is normally only known at xc2x1nxc2x72xcfx80, where n is a positive integer.
The object of the present invention is to realize a process in which the phase difference can clearly be determined. The object of the invention is achieved by a process characterized in that the period length for successive frequency sweeps is varied and in that the difference in period length and corresponding phase change is used to determine the velocity. By studying the phase change over a time period which can be made significantly shorter than the period length for a frequency sweep, the phase change can be kept within a clear interval.
The relative velocity v is advantageously calculated from the relationship:
v=kxc2x7x/xcex94T,
where x is the phase difference during the time xcex94T and       k    =                            c          /          2                ⁢                  xe2x80x83                ⁢        π                              2          ⁢                      xe2x80x83                    ⁢          α          ⁢                      xe2x80x83                    ⁢                      t            c                          +                  2          ⁢                      f            0                                ,      xe2x80x83    ⁢  where
c denotes the velocity of the light in air, xcex1 denotes the gradient of the frequency sweep, tc denotes the clock time and f0 denotes the carrier frequency of the signal.
The period length from a first to a second frequency sweep is changed by an amount less than or equal to the time difference which is required to be able clearly to determine the phase change on the basis of given limit values for distance apart, velocity and acceleration.
At least three successive frequency sweeps are expediently assigned a different period length.
In order to increase the accuracy in the velocity determination, the time interval during which the phase change is studied is progressively increased without any loss of clarity. An advantageous process is characterized in that phase changes, over and above for differences in period lengths, are studied for one or more period lengths and/or one or more added period lengths.